Kuznetsova survived a match point to beat world number four Agnieszka Radwanska 1-6 7-6(9) 6-4 in a thriller and Cibulkova edged Czech Barbora Strycova 6-3 3-6 6-4 in another tight duel.

Fourth seed Halep twice battled back from an early break before finding her rhythm, helped by Keys' 24 unforced errors, to wrap up the match in just over an hour.

Halep joins Germany's world number one Angelique Kerber, who was knocked out by Kvitova in the last 16 in China, and Serena Williams at the WTA Finals in Singapore.

"It means a lot to qualify... it was one of my goals this year," said Halep. "It will be my third time in a row competing at the WTA Finals and I hope I play great."

Kvitova, who made 24 unforced errors, had to rely on her powerful service game, which included seven aces, as Konta failed to break during the 1-1/2 hour encounter.

Kuznetsova again got the better of Radwanska, having lost just once in eight meetings with the Pole, as she came back from a set down to win a near three-hour battle.

Cibulkova gave a gutsy performaance to beat Strycova after both players turned out for both their third round and quarter-final matches on Thursday after rain affected Wednesday's play.

After completing a 6-2 6-2 upset win over fifth seed Karolina Pliskova in the first match of the day, Cibulkova was back on court for the last one against Strycova, who earlier claimed a 1-6 6-4 7-5 comeback win against Jelena Jankovic.

(Reporting by Shravanth Vijayakumar in Bengaluru; Editing by Ken Ferris)

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